IN CLOUDo AND RIVERS, ICE AND GLACIERS. 



103 



that the glacier is retarded not only by its 

 sides but by its bed ; that the upper portions 

 of the ice slide over the lower ones. Now if 

 Ihe bed of the Mar de Glace should have emi- 

 nences here aud there rising sufficiently near 

 to the surface to retard tile motion of the 



malning ones in twenty-four hours. 

 DAILY MOTION OF THE MER DE GLACE. 

 FIRST LINE : A A' UPON TUB SKETCH. 

 Eist West 



Stake 1 2 3 4 5 7 9 10 



Inches 12 17 23 26 25 26 27 33 



165. You have already assured yourself surface, they might produce the small irregu- 

 by actual contact that the body of the glacier larities noticed above. 



is real ice, and you may have read that 169. We note particularly, wliib upon t!ie 

 glaciers move : but the actual observation of ice, that the 26th stake, like the 10th stake 

 the motion of a body apparently so rigid is in our last line, stands much nearer to the 

 strangely interesting. And not only does the eastern than to the western side of the 

 fee move bodily, but one part of it moves glacier; the ni-.MSiiremni s, therefore, off or 

 past another ; the rate of motion augmenting a further proof that the centre of this portion 

 gradually from 12 inches a day at the side to of the glacier is nol the place of swiftest mo- 

 33 inches a day at a distance from the side. ' 

 This quicker movement of the central ice of 

 glaciers had been already observed by Agas- 

 siz and Forbes ; we verify their res-tilts, and 

 now proceed to something new. Crossing 

 the" Glacier du Geant, which occupies more 

 than half the valley, we find that our line of 

 stak?s is not yet at an end. The 10th stake 

 stands on the part of the ice which comes 



tion. 



23. UNEQUAL MOTION OF THE TWO SIDES 

 OF THE ME u DE GLACE. 



170. But in neither the first line nor the 

 second were we able to push our measure- 

 across the glacier. Why? In 

 to do one thing we are often 

 taught another, and thus in science, if ,ve 

 are only steadfast in our wort?, our very de- 

 feats are converted into means of instruc- 

 tion. We at first planted our theodolite on 

 the lateral moraine of the Mer de Glace, ex- 



friction of the sides is least, the motion ought - $ **J^ nowtot- 



from the Talrfre. 



106. Now the motion of the sides is slow, 

 because of the friction of the ice against its 

 boundaries ; but then one would think that 

 midway between the boundaries, where the 



VUSSi. Si? SSftS"Mffi =; U,e eentS ^ ScEp, to U= 



ft5S^^^^.gSrS^tf^g 



inches a da" 81te S1 ? e * lll(i gl acier was intercepted by the 



167. Here we have something to think of ; elevatioa ^ " c < re - T " e 

 but before a natural philosopher can think 

 with comfort he must be perfectly sure of 

 his facts. The foregoing line ran across the 



glacier a little below 

 Will 



the Montanvert. We 



and to multiply our chances of discovery we 



place along it 31 stakes. On the subsequent which we sweep the 



dav five of these were found unfit for IISP 



at the centre. The mountain- 

 slopes, in fact, are warm in summer, ami 

 they melt the ice nearest to them, thus caus- 

 ing a fall from the centre to the sides. 



171. But yonder on the heights at the 

 other side of the glacier we see a likely place 

 for our theodolite. We cross the glacier and 

 plant our instrument in a position from 

 glacier from side to 



side. Our first fine was below the Montan- 

 vert, our second line above it ; this third line 

 is exactly opposite the Montanvert ; in fact, 

 the mark on which we have fixed the fibre- 

 cross of the theodolite is a corner of one of 

 the windows of the little mn. Along this 

 line we fix twelve stakes on July 20th. On the 

 21st one of them had fallen : but the vi-loci 

 ties of the remaining eleven in 24 hours were 

 found to be as follows : 



THIRD LINE : C C' UPON TUB SKETCH. 



East We*t 



Stake, 1 23456789 10 11 



luches 20 23 29 30 34 28 25 23 25 18 9 



172. Both the first stake and the eleventh 



18th ; from 23 inches at the 19th we fall to in this series stor)d near the si(ics cf tbe , a _ 

 from 2o inches at the ----- ^ - - i ., .. . e 



remaining six-and-tvventy in 24 hours. 

 B B' UPON THE SKETCH. 



SECOND LINE 

 West 



3 4 5 

 12 15 15 

 16 17 18 

 23 23 21 



Stake... 2 

 Inches.. 11 

 b take... lo 

 Iaches..23 



East 



168. Look at these numbers. The first 

 broad fact Ihev reveal is the advance in the 

 rate of motion from first to last. There are, 

 however, small irregularities ; from 2'3 inches 

 at the 17th stake we fall to 21 inches at the 



21 inches at the 20th 



21st we fall to 22 inches at the 22d and 



23d ; but notwithstanding these small ups 



cier. On the eastern side the motion is 20 

 inches, while on the western side it is only 0. 

 It rises on the eastern side from 20 to 34 



and downs, the general advance of the rate inchGS at lhe 5th stake wliicu we standillg 



f motion is manifest Now there may have upon thc glacier can see to be much ucare r 



been some slight displacement of the stakes to l tho cas f ern lh ' an to the westem side . T/lc . 



by melting surhcient to account for these unitcd evidence of these three lines places tl* 



small deviations from uniformity in the in- factbeyond doubt, that opposite the Mwitanvert, 



crease of the motion But another solution and for some distance above it and below it, tte 



is also possible. We shall afterward learn ^ole eastern side of the glacier is mooing more 



